1. Field of the Invention
The present invention is in the field of methods for effecting sterilization of medical devices; more particularly, this invention is in the field of methods for sterilizing medical devices by the circulation of a sterilant gas over and through the device, wherein the sterilant gas remains within the lumen of the apparatus for an effective period of time.
2. Description of the Prior Art
The need to sterilize instruments and apparatus for use in medicine, agriculture and fermentation industries was known even before the germ theory of disease was established. Heat, steam and a variety of chemicals were observed to be able to inactivate spoilage and disease-producing entities; many machines and methods of applying these sterilizing agents entered the literature in the early years of microbiology. In recent years, steam and ethylene oxide vapor have become the most widespread sterilizing agents, with the latter being used primarily to treat materials which are susceptible to damage by heat or moisture. It is important in such processes to supply the necessary concentrations of steam or vapor for sufficient times at elevated temperatures to inactivate all the microorganisms both on and within the material being tested.
The use of ethylene oxide to sterilize heat-sensitive medical equipment was first described thirty years ago, in Kaye, S.: The Use of Ethylene Oxide for the Sterilization of Hospital Equipment; J. Lab. Clin. Med. vol. 35, 823-828 (1950). Since that time, this has become the only practical alternative to heat treatment, and the requirements for successful sterilization have been thoroughly documented. There are required, at the contaminated surface, the following:
(1) A sufficient concentration of ethylene oxide vapor PA1 (2) A relative humidity of between 20% and 70% PA1 (3) As high a temperature as the goods will stand PA1 (4) Enough exposure time to effect sterilization, and PA1 (5) Time to desorb the gas from the materials which absorb it, in order to eliminate toxic effects when the instrument is used.
The importance of each and all of these parameters has been discussed in hundreds of publications and dozens of patents, whose contents are known to those skilled in the art of sterilization. Where the objects to be sterilized possess simple configurations, so that gas, heat and moisture may readily reach all contaminated areas, they may simply be placed in a chamber where these conditions are met, and no problems arise. However, even with objects whose contaminated surfaces are readily accessible to the sterilizing atmosphere, a great many precautions must be taken to assure sterilization. These precautions include, e.g., the removal of air from the sterilizer chamber to as great a degree as possible or practical, provision of packaging materials permeable to the sterilizing agent, arrangement of packaged goods to facilitate contact by the sterilizing agent with the object, etc.
Efforts have been made in designing objects which require sterilization to make it easy for sterilizing vapors to contact, diffuse, permeate, or penetrate into all the internal as well as the external contaminated sites. However, due to their purpose and nature, some medical devices necessarily contain very long and very narrow tubules, or lumens, requiring heating and penetration by sterilizing vapors, which vapors must also contact all of the exterior surfaces of the device. Examples of such devices are catheters and endoscopic instruments. Endoscopes are included in the class of instruments which ordinarily cannot be sterilized in an autoclave. Because they must be inserted into a natural orifice or an incision, endoscopes are necessarily small, ranging up to no more than about 16 millimeters (mm) in diameter at the end used for insertion, treatment or manipulation. Within the main tube are disposed other tubes for viewing, illumination, irrigation and suction; each of these tubes is therefore smaller than the outer tube, and may be of the order of 1 mm.
In instruments such as endoscopes, therefore, there is considerable delay in achieving all the desired conditions for effective ethylene oxide sterilization; thus, water, heat, and ethylene oxide vapor take a considerable time to reach the contaminated locations within the narrow lumens of long tubes, and there is a concomitantly longer time required for the toxic sterilizing gas to diffuse out of such passages. This invention is directed to a method for speeding up contact of heat, gas, and water vapor to such inaccessible locations, and for removing the gas rapidly after sterilization has been accomplished.